The invention relates to a method according to the species of the main claim.
Ordinary automatic transmission controls of motor vehicles powered by internal combustion engines, as a rule initiate a reduction of the gear ratio when the accelerator pedal is released. When traveling on curves or when braking, however, this is not always desirable, since such a load change under certain conditions could lead to unsafe driving states, or, upon reacceleration of the motor vehicle by pressing on the accelerator pedal again, an increase in the gear ratio must be forced.
From DE 33 41 652 C2, in this connection and in connection with automatically shifted multi-step transmissions, it is known that this reduction of the gear ratio (upshifts) on curves can be avoided by determining the transverse acceleration of the motor vehicle. However, this only permits avoiding shifting on curves.
In order to be able to deliberately prevent reduction of the gear ratio when approaching curves, in the method for controlling an automatically shifting transmission according to DE 39 22 040 A1 the rate of change in the position of the accelerator pedal is recorded and, when a certain (negative) boundary value is undershot, a signal is derived to suppress an upshift process, provided coasting operation is recognized. Thereupon, upshifts are prevented until acceleration occurs again and a fixed time interval has elapsed.
It is also provided in DE 39 22 051 A1 to make this time interval dependent upon another parameter (driving activity), which is derived from one or a combination of several operating or driving parameters of a motor vehicle and evaluates a driving style of a driver or a prevailing traffic situation.
On the basis of this prior art, the goal of the invention is to provide a method for controlling a preferably electrohydraulically actuated continuously variable transmission for a motor vehicle that is further improved especially as regards the behavior of the adjustment of the gear ratio or the engine rpm before curves and when braking.
The goal is achieved according to the invention by the characterizing features of claim 1. Additional features that characterize the invention are contained in the subclaims.
The advantages of the invention lie primarily in the fact that a method for controlling a preferably electrohydraulically continuously variable transmission for a motor vehicle is provided, in which the adjusting behavior of the gear ratio, especially before curves and when braking, is further improved.
As soon as a state of a gear ratio determination is active, the gear ratio is set, or alternatively, either adjusted with a certain first relatively low speed or adjusted in such fashion that the engine rpm of a driving internal combustion engine changes with a predetermined rate (decreases). The state of the gear ratio determination becomes active when the driver of the motor vehicle, for example when approaching a curve, suddenly no longer presses down on the accelerator pedal and coasting operation is recognized. The state changes to the inactive state when, after acceleration is determined, a certain time interval has elapsed.
By virtue of an additional, renewed delay of changes in the gear ratio following recognition of acceleration followed by a new transition to coasting during a certain time interval, the driver of a motor vehicle, whose transmission is equipped with such a control, can briefly step on the accelerator even before curves without the undesired reduction of the gear ratio being performed. In this manner, improper estimates by the driver regarding approach to or travel around curves can be tolerated without negative effects on the overall driving behavior of the vehicle.
In another embodiment of the invention it is provided that after the end of the gear-ratio determination, a rapid adaptation of the gear ratio or of the engine rpm in the direction of a reduction is avoided over a large range, while the gear ratio or the engine rpm is adjusted at a certain second rate, whereby the latter is greater than the first rate but less than the maximum possible adjustment rate of the gear ratio of the continuously variable transmission.
Likewise, in braking, when certain noncritical conditions are present, an increase in gear ratio at a final third speed is automatically performed, whereby here again the adjustment rate is less than the maximum adjustment rate.
Maintenance of conditions ensures safe operation of the motor vehicle. Thus in particular monitoring ensures that the transverse acceleration is not too high, the vehicle is not decelerated too sharply, and the driving speed is not too high in order to prevent loss especially of the longitudinal and lateral guiding forces of the wheels of the motor vehicle. The braking moment, which acts increasingly on the driving wheels after an increase in gear ratio, of the driving (internal combustion) engine can therefore not have a negative effect on the driving behavior of the motor vehicle.
Increasing the gear ratio upon braking is preferably initiated when a state of gear-ratio determination is active. This is activated in known fashion when the motor vehicle approaches a curve and the driver no longer presses down on the accelerator pedal.
By increasing the gear ratio upon braking, firstly the braking effect of the driving engine of the motor vehicle is reinforced in coasting operation so that the brake (service brake) of the motor vehicle is relieved of its load. On the other hand, in conjunction with a determination of the gear ratio, provision is made, in and after curves, such that the driver, after passing through a curve, always has the optimum gear ratio or engine rpm available for reaccelerating the motor vehicle.
The invention will be explained below with reference to the embodiments shown in the drawings.